It is known to provide a pair of glass sheets with an aqueous gel therebetween, which under the action of heat radiation is transformed into an insulating foam.
Merely providing an aqueous gel between two sheets of glass is insufficient to provide a glazing unit which renders a window fire proof for a sufficient period of time to permit escape or assistance to arrive.
The prior art gels which are currently utilized in glazing units fail to take into consideration utilization of the glass panes at low temperatures and in locations of repeated shock. Moreover, these gels become cloudy at low temperatures and require heating means to maintain optical clarity.
Some of the problems with many of the prior art fire proof panes is that high heat causes the panes to shatter and expose the aqueous gel to the flames. With high intense heat the first pane shatters exposing both the gel and the second pane to high heat. Shattering of both panes does not provide any surface for the gel to remain in place. Consequently, the double pane glasses do not provide sufficient fire deterency and cannot be utilized in security installations.
In security installations that are presently being utilized, transparent laminates of glass, polyurethane, polycarbonate and ionomers are used as protective barriers. Moreover, optically transparent laminates which are used in prisons, psychiatric installations and commercial buildings must not only be resistant to physical and ballistic attacks, but capable of withstanding high heat and direct flames for a prolonged period of time to permit people to move to safety or for assistance to arrive. This combination of impact resistance and fire resistance has been difficult to achieve.
To provide security or armor glass with resistance to cracking and breaking during high heat and flames, it was common to include in the glass pane a wire mesh. However, such a solution to the problem resulted in a loss of transparency and aesthetic appearance. Moreover such windows cracked readily to permit heat to reach the other side of the window.
Other methods for forming fire resistant windows include providing an intumescent gel layer sandwiched over the outer sheets with a space that allows for expansion, as taught in French Patent No. 2,321,575.
In British Patent No. 1,354,497 there is disclosed a fire-proofing glass reinforced plastic which is formed by adding woven glass roving to a surface and applying a resin absorbing tissue and a coating of an intumescent gel. However, the optical clarity is affected.
It is known to make fire resistant panes for non-security installations by placing between two sheets of glass a solid layer of a product which under the action of heat radiation is transformed into an insulating foam, for example a hydrated alkaline silicate. Such panes are described in French Patent No. 2,027,646. Such panes have poor optical transparency and are not reliable for long periods of time. Also, the panes cannot deter physical attack.
U.S. Pat. No. 4,264,681 discloses an aqueous acrylic gel which utilizes an adherence gel to anchor the aqueous acrylic gel to the surface of glass panes. The adherence gel consists of organic titanates, organic zirconates and silanes which react with the double bonds of the acrylic gel.
British Patent No. 1,541,371 discloses a gel for use between glass panes which comprises an acrylic acid derivative and a foaming agent which an alkali metal or the ammonium salt of aluminates, silicates, stannates, plumbates, alums, borates or phosphates. The aqueous acrylic gel forms a heat insulating foam after the window breaks and the gel is exposed to high heat.
U.S. Pat. No. 4,799,346 to Bolten et al, which is herein incorporated by reference, discloses a laminated glazing unit that is interposed between outer sheets of glass or plastic and sets forth ionomer which is useful in the present invention.